Propeller assembly and pitch control unit

ABSTRACT

A variable pitch propeller assembly operatively coupled with an engine and methods for controlling the pitch of a plurality of propeller blades thereof is provided. In one example aspect, the variable pitch propeller assembly includes features for combining overspeed, feathering, and reverse functionality in a single secondary control valve. The secondary control valve is operable to selectively allow a controlled amount of hydraulic fluid to flow to or from a pitch actuation assembly such that the pitch of the propeller blades can be adjusted to operate the variable pitch propeller assembly in one of a constant speed mode, a feather mode, and a reverse mode.

RELATED APPLICATIONS

This patent claims the benefit of priority to U.S. patent applicationSer. No. 16/920,159, filed on Jul. 2, 2020, entitled “PROPELLER ASSEMBLYAND PITCH CONTROL UNIT,” which claims priority to Italian PatentApplication No. 102019000010929, filed on Jul. 4, 2019, entitled“PROPELLER ASSEMBLY AND PITCH CONTROL UNIT,” both of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to propeller control units.

BACKGROUND

Variable pitch propeller assemblies for aircraft are operativelyconfigured to adjust propeller blades of the propeller assembly througha plurality of blade angles. In this manner, the propeller blades can beadjusted to a propeller blade angle that optimizes engine performancefor given flight conditions or for ground operations. To adjust thepropeller blade angle of the propeller blades, variable pitch propellerassemblies typically include a pitch control unit. Certain pitch controlunits can include a primary pitch control valve or governor. Based onone or more input signals, the primary control valve selectively allowsan amount of hydraulic fluid to flow to or drain from a pitch actuationassembly positioned within the propeller assembly. By altering theamount of hydraulic fluid in the pitch actuation assembly, the bladeangle of the propeller blades can be set to the desired pitch.

For constant-speed variable pitch propeller assemblies, the pitchcontrol unit is configured to maintain constant engine speed byadjusting the propeller blade angle to vary the load on the propeller inresponse to changing flight conditions. In particular, the primarycontrol valve modulates the pitch of the propeller blades to keep thereference speed. In some instances, the propeller assembly canexperience an overspeed condition, which occurs when propeller RPMincreases above the reference speed, and in some instances, thepropeller assembly can experience an underspeed condition, which occurswhen propeller RPM decreases below the reference speed. When anoverspeed or underspeed condition is experienced, the primary controlvalve controls the flow of hydraulic fluid through the system such thatthe propeller assembly returns to an onspeed condition, or a conditionin which the actual RPM of the engine is the same as the referencespeed.

Moreover, some variable pitch propeller assemblies are configured asfeathering propeller assemblies. Such feathering propeller assembliestypically include a solenoid-operated feather valve. Thesolenoid-operated feather valve is operatively configured to switch thepropeller assembly into a feather mode. The feathering mode can becommanded by a pilot by a dedicated cockpit switch, can be commanded byan engine controller after a normal shutdown, or can be commandedautomatically by the engine controller (i.e., autofeather) when anengine flames out or an unexpected sudden reduction of power isdetected. Such conventional solenoid-operated feather valves andaccompanying sensing components can increase the weight of the engine,which is a penalty on the efficiency of the engine.

In addition, some variable pitch propeller assemblies include groundbeta or reverse mode functionality. For instance, some propellerassemblies include a ground beta enable solenoid and a ground betaenable valve that effectively enable the propeller blades to move to afine pitch position, e.g., for taxiing on the ground, or a reverseangle, e.g., for reverse and braking. These conventional solenoids andvalves can increase the weight of the engine, which is a penalty on theefficiency of the engine.

BRIEF DESCRIPTION

The present disclosure relates to a variable pitch propeller assemblyfor an engine defining an axial direction, a radial direction, and acircumferential direction, the variable pitch propeller assemblyincluding a plurality of propeller blades rotatable about the axialdirection and spaced apart along the circumferential direction, eachpropeller blade rotatable through a plurality of blade angles aboutrespective pitch axes each extending in the radial direction, a pitchactuation assembly for adjusting the plurality of propeller bladesthrough the plurality of blade angles and including a propeller domedefining a chamber, and a pitch control unit, including at least oneelectrohydraulic servovalve operable to selectively allow a flow ofhydraulic fluid to or from the propeller dome of the pitch actuationassembly and when hydraulic fluid is not located at an inlet port of theat least one electrohydraulic servovalve an oil starvation condition isdefined, and at least one valve selectively fluidly coupling thepropeller dome to the inlet port of the at least one electrohydraulicservovalve. Any permutation of aspects of the disclosure can alsoinclude wherein the at least one valve is a one-way valve having aninlet fluidly coupled to the propeller dome and an outlet fluidlycoupled to the inlet port of the at least one electrohydraulicservovalve and during the oil starvation condition the one-way valve isconfigured to fluidly couple the propeller dome to the inlet port of theat least one electrohydraulic servovalve. Any permutation of aspects ofthe disclosure can also include wherein the at least oneelectrohydraulic servovalve is a primary pitch control valve having afirst stage and a second stage and the one-way valve is selectivelyfluidly coupled with the first stage. Any permutation of aspects of thedisclosure can also include wherein the plurality of propeller bladesmove to a feather mode during the oil starvation condition at a lowerspeed as compared the pitch control unit without the at least one valve.

Any permutation of aspects of the disclosure can also include whereinthe at least one valve is a pitch lock valve having an inlet fluidlycoupled to the propeller dome and a set of outlets and during the oilstarvation condition the pitch lock valve is configured to fluidlyuncouple the propeller dome to the inlet port of the at least oneelectrohydraulic servovalve. Any permutation of aspects of thedisclosure can also include wherein the at least one electrohydraulicservovalve includes a primary control valve operable to selectivelyallow a flow of hydraulic fluid to or from the pitch actuation assemblyand a secondary control valve adjustable between a constant speed mode,a feather mode, and a reverse mode and operable to selectively allow aflow of hydraulic fluid to or from the pitch actuation assembly based atleast in part on the mode of the secondary control valve. Anypermutation of aspects of the disclosure can also include wherein theset of outlets includes a first outlet fluidly coupled to a first stageof the primary control valve, a second outlet fluidly coupled to a firststage of the secondary control valve, and a third outlet fluidly coupleda drain line. Any permutation of aspects of the disclosure can alsoinclude wherein the pitch lock valve includes a valve body moveablebetween a first position wherein the first outlet and the second outletare fluidly coupled with the inlet and a second position wherein thethird outlet is fluidly coupled to the inlet. Any permutation of aspectsof the disclosure can also include wherein the valve body is configuredto be moveable from the first position to the second position based on adecrease in internal pressure caused during the oil starvationcondition. Any permutation of aspects of the disclosure can also includea solenoid valve fluidly coupled between the third outlet and the drainline and operable to selectively open and close a flow of hydraulicfluid through the drain line. Any permutation of aspects of thedisclosure can also include wherein the solenoid valve is one of useractuated or automatically controller actuated. Any permutation ofaspects of the disclosure can also include wherein actuation of thesolenoid valve opens the flow of hydraulic fluid through the drain line.Any permutation of aspects of the disclosure can also include whereinthe secondary control valve includes a valve body defining a chamber anda spool movable within the chamber and where the spool defines a firstgroove and a second groove, and wherein the primary control valve isfluidly connected with the first groove when the spool is in at leastone constant speed position or in at least one reverse position.

Any permutation of aspects of the disclosure can also include whereinthe pitch actuation assembly includes a control piston translatablewithin the propeller dome, a piston rod connected to the control pistonand extending into a propeller gear box of the engine, the piston rodtranslatable in unison with the control piston, an oil transfer bearingsurrounding the piston rod within the propeller gear box of the engineand defining a flight gallery fluidly connected with the secondarycontrol valve and a ground gallery fluidly connected with the secondarycontrol valve, and a beta tube enclosed within the piston rod andfluidly connecting the flight gallery with the chamber of the propellerdome. Any permutation of aspects of the disclosure can also includewherein a flight gallery conduit fluidly connects the secondary controlvalve with the flight gallery and a ground gallery conduit fluidlyconnects the secondary control valve with the ground gallery.

The present disclosure also relates to a method for controlling avariable pitch propeller assembly driven by a powerplant, the powerplantdefining an axial direction and a radial direction and including acontroller, the variable pitch propeller assembly having a plurality ofpropeller blades rotatable about the axial direction and adjustableabout respective pitch axes each extending along the radial direction,the propeller control system including a pitch actuation assembly foractuating the propeller blades about their respective pitch axes and apitch control unit for driving the pitch actuation assembly andincluding a primary control valve and a secondary control valve bothcommunicatively coupled with the controller, the primary control valveand the secondary control valve each configured to selectively control aflow of hydraulic fluid to or from the pitch actuation assembly, themethod including operating the powerplant, controlling, by thecontroller, the secondary control valve adjustable between a constantspeed mode, a feather mode, and a reverse mode to selectively allow acontrolled amount of hydraulic fluid to or from the pitch actuationassembly, selectively diverting, during an oil starvation condition,hydraulic fluid from a propeller dome of the variable pitch propellerassembly via at least one valve. Any permutation of aspects of thedisclosure can also include wherein the at least one valve is a one-wayvalve having an inlet fluidly coupled to the propeller dome and anoutlet fluidly coupled to an inlet port of the primary control valve andduring the oil starvation condition the one-way valve provides fluidlycoupling from the propeller dome to the inlet port of the primarycontrol valve. Any permutation of aspects of the disclosure can alsoinclude controlling a feathering with the primary control valve upon afailure of the secondary control valve. Any permutation of aspects ofthe disclosure can also include wherein the at least one valve is apitch lock valve having an inlet fluidly coupled to the propeller dome,a first outlet fluidly coupled to a first stage of the primary controlvalve, a second outlet fluidly coupled to a first stage of the secondarycontrol valve, and a third outlet fluidly coupled a drain line and whereselectively diverting the hydraulic fluid includes moving a valve bodymoveable between a first position wherein the first outlet and thesecond outlet are fluidly coupled with the inlet or a second positionwherein the third outlet is fluidly coupled to the inlet. Anypermutation of aspects of the disclosure can also include whereinselectively diverting the hydraulic fluid from the propeller domefurther includes opening a valve on the drain line to create a feathercondition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an example gas turbine engine according to anexample of the present disclosure as described herein.

FIG. 2 is a perspective, cutaway view of the gas turbine engine of FIG.1 .

FIG. 3 is a schematic view of an example propeller control system of thegas turbine engine of FIG. 1 .

FIG. 4 is a schematic view of a propeller control unit of the propellercontrol system of FIG. 3 depicting a secondary control valve in aconstant speed mode.

FIG. 5 is a schematic view of the propeller control unit of FIG. 4depicting the secondary control valve in a feather mode.

FIG. 6 is a schematic view of the propeller control unit of FIG. 4depicting the secondary control valve in a reverse mode.

FIG. 7 is an example controller of the gas turbine engine of FIG. 1 .

FIG. 8 illustrates pitch control valve behavior in a normal mode and oilstarvation mode.

FIG. 9 is a schematic view of an example propeller control system of thegas turbine engine of FIG. 1 having an additional one-way valve.

FIG. 10 illustrates pitch control valve behavior in a normal mode andoil starvation mode in the system with the additional one-way valve.

FIG. 11 is a schematic view of an example propeller control system ofthe gas turbine engine of FIG. 1 with the pitch lock valve in a firstposition.

FIG. 12 is a schematic view of the propeller control unit of FIG. 11with the pitch lock valve in a second position and depicting a solenoidvalve in an opened condition that allows for feathering.

DETAILED DESCRIPTION

The present disclosure relates generally to variable pitch propellerassemblies and methods therefore for controlling the pitch of aplurality of propeller blades of a variable pitch propeller assemblyincluding during an oil starvation condition. In one example aspect, thevariable pitch propeller assembly includes features for combiningoverspeed, feathering, and reverse enabling functionality in a singleelectrohydraulic servovalve (EHSV). In particular, in one exampleaspect, a variable pitch propeller assembly includes a secondary EHSVcontrol valve operatively configured to protect the propeller assemblyand engine from an overspeed condition, and more generally formaintaining the propeller assembly and engine in an onspeed conditionduring flight, as well as providing feathering functionality in theevent a primary pitch control valve fails or is otherwise unresponsiveor operating conditions require it. Further, the secondary control valveis operatively configured to enable reverse functionality. That is, thesecondary control valve is configured to enable the propeller blades tobe actuated to a reverse pitch, e.g., to produce a reverse thrust. Thesecondary control valve is operable to selectively allow a controlledamount of hydraulic fluid to flow to or from a pitch actuation assemblysuch that the pitch of the propeller blades can be adjusted to operatethe variable pitch propeller assembly in one of a constant speed mode, afeather mode, and a reverse mode.

The present disclosure allows for methods and pitch control units thatselectively divert, during an oil starvation condition, hydraulic fluidfrom a propeller dome of the variable pitch propeller assembly via atleast one valve. This allows for the forestalling or preclusionaltogether of a feather mode. It is contemplated that an emergencyfeathering can be commanded if necessary.

As used herein, the terms “first,” “second,” and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.As used herein, “a set” can include any number of the respectivelydescribed elements, including only one element. The terms “upstream” and“downstream” refer to the relative direction with respect to fluid flowin a fluid pathway. For example, “upstream” refers to the direction fromwhich the fluid flows, and “downstream” refers to the direction to whichthe fluid flows. All directional references (e.g., radial, axial,proximal, distal, upper, lower, upward, downward, left, right, lateral,front, back, top, bottom, above, below, vertical, horizontal, clockwise,counterclockwise, upstream, downstream, forward, aft, etc.) are onlyused for identification purposes to aid the reader's understanding ofthe present disclosure, and do not create limitations, particularly asto the position, orientation, or use of the disclosure. Connectionreferences (e.g., attached, coupled, connected, and joined) are to beconstrued broadly and can include intermediate members between acollection of elements and relative movement between elements unlessotherwise indicated. As such, connection references do not necessarilyinfer that two elements are directly connected and in fixed relation toone another. The exemplary drawings are for purposes of illustrationonly and the dimensions, positions, order, and relative sizes reflectedin the drawings attached hereto can vary.

FIGS. 1 and 2 provide various views of an example engine 100 accordingto examples of the present disclosure. Particularly, FIG. 1 provides aside view of the engine 100 and FIG. 2 provides a perspective, cutawayview of the engine 100 of FIG. 1 . As shown in FIG. 1 , the engine 100is a gas turbine engine, and more specifically, a turboprop engine. Thegas turbine engine 100 defines an axial direction A, a radial directionR, and a circumferential direction C (FIG. 2 ) extending three hundredsixty degrees (360°) around the axial direction A. The gas turbineengine 100 also defines a longitudinal or axial centerline 102 extendingalong the axial direction A. The gas turbine engine 100 extendsgenerally along the axial direction A between a first end 103 and asecond end 105, which is the forward and aft end, respectively.Generally, the gas turbine engine 100 includes a gas generator or coreturbine engine 104 and a propeller assembly 106 rotatable about theaxial centerline 102, or more generally, the axial direction A.

As shown best in FIG. 2 , the core turbine engine 104 generallyincludes, in serial flow arrangement, a compressor section 110, acombustion section 112, a turbine section 114, and an exhaust section116. A core air flow path 118 extends from an annular inlet 120 to oneor more exhaust outlets 122 of the exhaust section 116 such that thecompressor section 110, combustion section 112, turbine section 114, andexhaust section 116 are in fluid communication.

The compressor section 110 can include one or more compressors, such asa high pressure compressor (HPC) and a low pressure compressor (LPC).For this example, the compressor section 110 includes a four-stageaxial, single centrifugal compressor. In particular, the compressorincludes sequential stages of compressor stator vanes and rotor blades(not labeled), as well as an impeller (not labeled) positioneddownstream of the axial stages of stator vanes and rotor blades. Thecombustion section 112 includes a reverse-flow combustor (not labeled)and one or more fuel nozzles (not shown). The turbine section 114 candefine one or more turbines, such as a high pressure turbine (HPT) and alow pressure turbine (LPT). For this example, the turbine section 114includes a two-stage HPT 126 for driving the compressor of thecompressor section 110. The HPT 126 includes two sequential stages ofstator vanes and turbine blades (not labeled). The turbine section 114also includes a three-stage free or power turbine 128 that drives apropeller gearbox 134, which in turn drives the propeller assembly 106(FIG. 1 ). The exhaust section 116 includes one or more exhaust outlets122 for routing the combustion products to the ambient air.

Referring still to FIG. 2 , the core turbine engine 104 can include oneor more shafts. For this example, the gas turbine engine 100 includes acompressor shaft 130 and a free or power shaft 132. The compressor shaft130 drivingly couples the turbine section 114 with the compressorsection 110 to drive the rotational components of the compressor. Thepower shaft 132 drivingly couples the power turbine 128 to drive a geartrain 140 of the propeller gearbox 134, which in turn operativelysupplies power and torque to the propeller assembly 106 (FIG. 1 ) via atorque output or propeller shaft 136 at a reduced RPM. The forward endof the propeller shaft 136 includes a flange 137 that provides amounting interface for the propeller assembly 106 to be attached to thecore turbine engine 104.

The propeller gearbox 134 is enclosed within a gearbox housing 138. Forthis example, the housing 138 encloses the epicyclical gear train 140that includes a star gear 142 and a plurality of planet gears 144disposed about the star gear 142. The planetary gears 144 are configuredto revolve around the star gear 142. An annular gear 146 is positionedaxially forward of the star and planetary gears 142, 144. As theplanetary gears 144 rotate about the star gear 142, torque and power aretransmitted to the annular gear 146. As shown, the annular gear 146 isoperatively coupled to or otherwise integral with the propeller shaft136. In some examples, the gear train 140 may further include additionalplanetary gears disposed radially between the plurality of planet gears144 and the star gear 142 or between the plurality of planet gears 144and the annular gear 146. In addition, the gear train 140 may furtherinclude additional annular gears.

As noted above, the core turbine engine 104 transmits power and torqueto the propeller gearbox 134 via the power shaft 132. The power shaft132 drives the star gear 142, which in turn drives the planetary gears144 about the star gear 142. The planetary gears 144 in turn drive theannular gear 146, which is operatively coupled with the propeller shaft136. In this way, the energy extracted from the power turbine 128supports operation of the propeller shaft 136, and through the powergear train 140, the relatively high RPM of the power shaft 132 isreduced to a more suitable RPM for the propeller assembly 106.

In addition, the gas turbine engine 100 includes one or more controllers280 that control the core turbine engine 104 and the propeller assembly106. For this example, the controller 280 is a single unit controldevice for a Full Authority Digital Engine (FADEC) system operable toprovide full digital control of the core turbine engine 104, and in someexamples, the propeller assembly 106. The controller 280 depicted in theillustrated example of FIGS. 1 and 2 can control various aspects of thecore turbine engine 104 and the propeller assembly 106. For example, thecontroller 280 can receive one or more signals from sensory or datacollection devices and can determine the blade angle of a plurality ofpropeller blades 150 about their respective pitch axes, as well as theirrotational speed about the axial direction A based at least in part onthe received signals. The controller 280 can in turn control one or morecomponents of the gas turbine engine 100 based on such signals. Forexample, based at least in part on one or more speed or blade pitchsignals (or both), the controller 280 can be operatively configured tocontrol one or more valves such that an amount of hydraulic fluid can bedelivered or returned from a pitch actuation assembly of the gas turbineengine 100 as will be described in greater detail herein. The internalcomponents of the controller 280 will likewise be described in detailherein.

With reference to FIG. 1 , during operation of the gas turbine engine100, a volume of air indicated by arrow 148 passes across the pluralityof propeller blades 150 circumferentially spaced apart from one anotheralong the circumferential direction C and disposed about the axialdirection A, and more particularly for this example, the axialcenterline 102. The propeller assembly 106 includes a spinner 163aerodynamically contoured to facilitate an airflow through the pluralityof propeller blades 150. The spinner 163 is rotatable with the propellerblades 150 about the axial direction A and encloses various componentsof the propeller assembly 106, such as e.g., the hub, propeller pitchactuator, piston/cylinder actuation mechanisms, etc. A first portion ofair indicated by arrow 152 is directed or routed outside of the coreturbine engine 104 to provide propulsion. A second portion of airindicated by arrow 154 is directed or routed through the annular inlet120 of the gas turbine engine 100.

As shown in FIG. 2 , the second portion of air 154 enters through theannular inlet 120 and flows downstream to the compressor section 110,which is a forward direction along the axial direction A in thisexample. The second portion of air 154 is progressively compressed as itflows through the compressor section 110 downstream toward thecombustion section 112.

The compressed air indicated by arrow 156 flows into the combustionsection 112 where fuel is introduced, mixed with at least a portion ofthe compressed air 156, and ignited to form combustion gases 158. Thecombustion gases 158 flow downstream into the turbine section 114,causing rotary members of the turbine section 114 to rotate, which inturn supports operation of respectively coupled rotary members in thecompressor section 110 and propeller assembly 106. In particular, theHPT 126 extracts energy from the combustion gases 158, causing theturbine blades to rotate. The rotation of the turbine blades of the HPT126 causes the compressor shaft 130 to rotate, and as a result, therotary components of the compressor are rotated about the axialdirection A. In a similar fashion, the power turbine 128 extracts energyfrom the combustion gases 158, causing the blades of the power turbine128 to rotate about the axial direction A. The rotation of the turbineblades of the power turbine 128 causes the power shaft 132 to rotate,which in turn drives the power gear train 140 of the propeller gearbox134.

The propeller gearbox 134 in turn transmits the power provided by thepower shaft 132 to the propeller shaft 136 at a reduced RPM and desiredamount of torque. The propeller shaft 136 in turn drives the propellerassembly 106 such that the propeller blades 150 rotate about the axialdirection A, and more particularly for this example, the axialcenterline 102 of the gas turbine engine 100. The exhaust gases, denotedby 160, exit the core turbine engine 104 through the exhaust outlets 122to the ambient air.

It should be appreciated that the example gas turbine engine 100described herein is provided by way of example only. For example, inother example examples, the engine may include any suitable number ortypes of compressors (such as e.g., reverse flow and/or axialcompressors), turbines, shafts, stages, etc. Additionally, in someexamples, the gas turbine engine may include any suitable type ofcombustor, and may not include the example reverse-flow combustordepicted. It will further be appreciated that the engine can beconfigured as any suitable type of gas turbine engine, including, forexample, turboshaft, turbojets, etc. Moreover, in yet other examples,the engine can be configured as a reciprocating or piston engine. Inaddition, it will be appreciated that the present subject matter can beapplied to or employed with any suitable type of propeller or fanconfiguration, including, for example, tractor and pusherconfigurations.

Furthermore, although the gas turbine engine 100 described above is anaeronautical gas turbine engine for propulsion of a fixed-wing aircraft,the gas turbine engine may be configured as any suitable type of gasturbine engine for use in any number of applications, such as marineapplications. Furthermore, the innovation could be used on other deviceswith variable pitch blades such as windmills. The propeller assembly 106may rotate due to passing of a fluid, such as air or water, across theplurality of blades 150 of the propeller assembly 106.

FIG. 3 provides a schematic view of an example propeller control system200 for controlling the propeller assembly 106 of the gas turbine engine100 of FIGS. 1 and 2 according to an example of the present disclosure.As depicted in FIG. 3 , the propeller assembly 106 is driven by the coreturbine engine 104 (FIG. 2 ) by the propeller shaft 136. The propellershaft 136 in turn drives a hub 162 from which the plurality of propellerblades 150 extend outwardly from in the radial direction R. As thepropeller shaft 136 rotates about the axial direction A, the hub 162 inturn rotates the propeller blades 150 about the axial direction A. Thepropeller control system 200 includes features for controlling therotational speed of the propeller blades 150 about the axial direction Aand the pitch of the propeller blades 150, as well as features forprotecting the components of the propeller assembly 106. As shown inFIG. 3 , the propeller control system 200 includes a pitch actuationassembly 202, a pitch control unit 204, a power lever 206, andcontroller 280.

Generally, the pitch actuation assembly 202 is operatively configured toadjust the plurality of propeller blades 150 through a plurality ofblade angles. Stated differently, the pitch actuation assembly 202 isoperatively configured to rotate each propeller blade 150 aboutrespective pitch axes P extending in the radial direction R (each pitchaxis P is relative to a corresponding propeller blade 150). For theexample of FIG. 3 , the pitch actuation assembly 202 is operativelyconfigured to rotate the plurality of propeller blades 150 between highor coarse pitch blade angles, including a fully feathered blade angle tolow or fine pitch blade angles. Moreover, for this example, the pitchactuation assembly 202 is additionally operatively configured to rotatethe plurality of propeller blades 150 through reverse pitch angles,which can be useful for ground or taxiing operations, particularly wherean aircraft includes multiple engines. In this regard, the examplepropeller assembly 106 depicted in FIG. 3 is a variable pitch, fullfeathering, and reverse enabled propeller assembly, and moreparticularly still, the propeller assembly is configured as a variablepitch constant-speed, full feathering, reverse enabled propellerassembly. A pilot or aircrew member can operate the propeller assembly106 in one of the modes noted above utilizing one or more levers. Forinstance, as shown in FIG. 3 , the aircraft to which the gas turbineengine 100 is operatively coupled includes control levers. Inparticular, for this example, the aircraft includes power lever 206. Thepower lever 206 can be set within a ground range GR (e.g., for taxiing),within a flight range FR, or within a feathering range FT (e.g., in theevent of engine failure). In some examples, the aircraft to which thegas turbine engine 100 is operatively coupled includes other controllevers, such as e.g., a condition lever, propeller speed levers, mixturelevers, etc.

As further shown in FIG. 3 , for this example, the pitch actuationassembly 202 includes a single-acting system for controlling oradjusting the pitch of the propeller blades 150. It will be appreciated,however, that the pitch actuation assembly 202 can be a double-actingsystem in other examples. The single-acting system pitch actuationassembly 202 of FIG. 3 includes a housing, cylinder or propeller dome166 that defines a chamber and encloses a control piston 168 that istranslatable along the axial direction A within the chamber of thepropeller dome 166. In particular, as shown, the propeller dome 166 andthe outboard side 169 of the control piston 168 define a first side 173of the chamber and the propeller dome 166 and the inboard side 167 ofthe control piston 168 define a second side 174 of the chamber. Thecontrol piston 168 separates the first side 173 from the second side 174of the chamber along the axial direction A. The control piston 168 isbiased on its outboard side 169 by a feather spring 172 positionedwithin the first side 173 of the chamber, as well as by one or morecounterweights 182 operatively coupled with one or more propeller blades150.

The control piston 168 is operatively coupled with a piston rod 184 thatextends along the axial direction A. In particular, the piston rod 184extends from the propeller assembly 106 (where the piston rod 184 isconnected to the control piston 168) to the propeller gearbox 134 alongthe axial direction A. The piston rod 184 and the control piston 168 aretranslatable in unison. The piston rod 184 encloses an oil transfer orbeta tube 170 that also extends along the axial direction A. When thepropeller blades 150 are rotated about the axial direction A, the pistonrod 184 and the beta tube 170 are likewise rotatable about the axialdirection A. Like the piston rod 184, the beta tube 170 extends at leastpartially into the propeller assembly 106 and at least partially intothe propeller gearbox 134 positioned within the gearbox housing 138(FIG. 2 ). To control the blade angles of the propeller blades 150,hydraulic fluid (e.g., oil) can be fed through the beta tube 170 and/orother fluid channels to the second side 174 of the chamber (or to thefirst side 173 of the chamber in a double-acting system) to translatethe control piston 168 along the axial direction A. The beta tube 170can define one or more orifices 176 that permit hydraulic fluid to flowfrom the hollow beta tube 170 to the second side 174 of the chamberdepending on the desired blade pitch. Hydraulic fluid can enter and exitthe beta tube 170 through an oil transfer bearing 186 surrounding thepiston rod 184 within the propeller gear box 134. The oil transferbearing 186 defines an annular flight gallery 221 and an annular groundgallery 222.

With reference still to FIG. 3 , during operation of the gas turbineengine 100 the spring 172 and the counterweights 182 constantly urge thecontrol piston 168 along the axial direction A (a direction to the rightin FIG. 3 ) such that the propeller blades 150 operatively coupled withthe control piston 168 (e.g., by the piston rod and an actuation levercoupled thereto) are driven toward a coarse or high pitch position.

To actuate the propeller blades 150 toward a low or fine pitch position,an amount of hydraulic fluid is delivered to the second side 174 of thechamber such that a force sufficient to overcome the biasing force ofthe spring 172 and the counterweights 182 is applied to the inboard side167 of the control piston 168. The hydraulic force on the inboard side167 of the control piston 168 actuates the control piston 168 along theaxial direction A (a direction to the left in FIG. 3 ). This in turncauses the piston rod 184 and enclosed beta tube 170 to translateforward along the axial direction A (or toward the left in FIG. 3 ).When the control piston 168 is moved forward along the axial directionA, the propeller blades 150 are rotated to a more fine or low pitchposition. When rotated to a more fine position, the propeller blades 150take less “bite” out of the air when the propeller is operating in aforward mode. In a reverse mode, the propeller blades 150 take a greater“bite” out of the air when rotated to a more fine position.

When it is desired to adjust the angle of the propeller blades 150 backtoward coarse or high pitch, an amount of hydraulic fluid within thesecond side 174 of the chamber is returned or scavenged back to theengine (e.g., via one of the drains 224) such that the spring 172 andthe counterweights 182 can urge the control piston 168 rearward alongthe axial direction A (a direction to the right in FIG. 3 ). Thehydraulic fluid can drain through the beta tube 170 and to the oiltransfer bearing 186 positioned within the propeller gearbox 134. Thehydraulic fluid can then be drained to a sump or other like structure.When rotated to a more coarse position, the propeller blades 150 take agreater “bite” out of the air when the propeller is operating in aforward mode. In a reverse mode, the propeller blades 150 take less“bite” out of the air when rotated to a more coarse position.

The translation of the control piston 168 along the axial direction A inturn causes the piston rod 184 to translate along the axial direction Aas well. To move the propeller blades 150 about their respective pitchaxes P, the propeller assembly 106 includes a pitch actuation orpropeller pitch actuator 178 to pitch or actuate the propeller blades150. When the control piston 168 is translated along the axial directionA, the propeller pitch actuator 178, which is operatively coupled to thepiston rod 184, rotates the propeller blades 150 about their respectivepitch axes P.

Accordingly, the axial position of the piston rod 184 and beta tube 170corresponds with a particular blade angle or angular position of thepropeller blades 150.

As further shown in FIG. 3 , the piston rod 184 encloses beta tube 170as well as the propeller pitch actuator 178 operatively coupled thereto.The piston rod 184 is operatively coupled with the propeller pitchactuator 178, which in this example includes an actuation lever 180. Theactuation lever 180 is operatively coupled to the plurality of blades150 such that movement of the actuation lever 180 along the axialdirection A moves or rotates the plurality of blades 150 about theirrespective pitch axes P. Stated alternatively, as the piston rod 184 andenclosed beta tube 170 translate along the axial direction A (caused bythe axial displacement of the control piston 168), the actuation lever180 also translates along the axial direction A. This in turn causes theplurality of blades 150 to rotate about their respective pitch axes P,thereby adjusting the blade angles of the propeller blades 150 to thedesired pitch. Thus, by controlling the quantity of hydraulic fluidwithin the second side 174 of the chamber, the propeller blades 150 canbe controlled through a plurality of blade angles about their respectivepitch axes P by the actuation lever 180.

It will be appreciated that the propeller pitch actuator 178 may includeadditional or alternative structures that provide pitch actuationfunctionality. For example, such structures may include actuationlinkages linking the control piston 168, piston rod, or other axiallydisplaceable components with the propeller blades 150. Other structuresmay include a yoke and cam assembly operatively coupled with the betatube 170 and/or piston rod 184 enclosing the beta tube 170. Any suitablestructure can be used to rotate the propeller blades 150 about theirrespective pitch axes P. Stated alternatively, any known assemblies orstructures for converting the translatory motion of the piston rod 184into rotational motion of the propeller blades 150 is contemplated.

As further depicted in FIG. 3 , an example pitch control unit 204 of thepropeller control system 200 is provided. Generally, the pitch controlunit 204 is operatively configured to provide an amount of hydraulicfluid to the pitch actuation assembly 202 such that the pitch actuationassembly 202 can adjust the plurality of propeller blades 150 through aplurality of blade angles. More specifically, the pitch control unit 204is operatively configured to deliver or return an amount of hydraulicfluid from the second side 174 of the chamber such that the controlpiston 168 is translated along the axial direction A, which in turndrives the piston rod 184 along the axial direction A, causing thepropeller pitch actuator 178 to adjust the plurality of propeller blades150 about their respective pitch axes P.

The pitch control unit 204 includes a high pressure pump 210 positioneddownstream of and in fluid communication with a lubrication supply 212,such as e.g., hydraulic fluid from the engine. The lubrication supply212 is configured to supply hydraulic fluid, such as e.g., oil, to thepropeller control system 200. The high pressure pump 210 is operativelyconfigured to increase the pressure of the hydraulic fluid as it flowsfrom the lubrication supply 212 downstream to the components of thepropeller control system 200. A lubrication supply conduit 214 providesfluid communication between the lubrication supply 212 and the highpressure pump 210.

A pressure relief valve 216 is positioned downstream of the highpressure pump 210 and is in fluid communication with the high pressurepump 210. The pressure relief valve 216 is in fluid communication withthe high pressure pump 210 via a high pressure (HP) conduit 218. Thepressure relief valve 216 is operatively configured to regulate thepressure of the hydraulic fluid within the propeller control system 200.In the event the pressure of the hydraulic fluid within the HP conduit218 exceeds a predetermined threshold, the pressure relief valve 216 candrain an amount of hydraulic fluid from the HP conduit 218. Inparticular, the pressure of the hydraulic fluid acting on the controlpiston of the pressure relief valve 216 overcomes a spring biasing forceapplied by a spring of the pressure relief valve 216, allowing an amountof hydraulic fluid to drain from the system, as indicated by 224. Thehydraulic fluid can then be scavenged to the lubrication supply 212, forexample.

With reference still to FIG. 3 , the pitch control unit 204 includes aprimary pitch control valve 230. The primary control valve 230 isoperatively configured to adjust the propeller pitch or blade angles ofthe propeller blades 150 during normal operation of the engine. For thisexample, the primary control valve 230 is a spool-type directional EHSV.The primary control valve 230 is positioned downstream of and is influid communication with the high pressure pump 210. In particular, theprimary control valve 230 is in fluid communication with the highpressure pump 210 via the HP conduit 218. A first portion of the highpressure hydraulic fluid from the high pressure pump 210 is delivered toa first stage 231 of the primary control valve 230, which is a doublenozzle-flapper valve that includes a toque motor, a flapper, twonozzles, and a feedback spring. A second portion of the high pressurehydraulic fluid from the high pressure pump 210 is delivered to a secondstage 232 of the primary control valve 230, which is a precision controlspool valve. The second stage 232 of the primary pitch control valve 230has a valve body 235 defining a chamber and a spool 233 movable withinthe chamber. The first portion of the high pressure hydraulic fluiddelivered to first stage 231 can be used to actuate the second stage 232precision control spool. In this way, the primary control valve 230 canselectively control or allow a flow of hydraulic fluid to or from thepitch actuation assembly 202. For instance, the first stage 231 cancontrol the spool 233 of the second stage 232 to actuate or remain in anull position depending on the condition in which the propeller isoperating. At times, if there is excess hydraulic fluid within theprimary control valve 230, the fluid can be scavenged to the lubricationsupply 212, for example, as denoted by drain 224.

Generally, the propeller assembly 106 operates in one of threeconditions while the aircraft is in flight, including an onspeedcondition, an overspeed condition, or an underspeed condition. Anonspeed condition results when the engine is operating at the RPM set bythe pilot. An overspeed condition results when the engine is operatingabove the RPM set by the pilot. As an example, if the aircraft begins topitch downward into a descent maneuver, the airspeed increases acrossthe propeller blades. When this occurs, the propeller blades are unableto fully absorb the engine power, and as a result, the engine RPMincreases above the desired setting resulting in an overspeed condition.An underspeed condition results when the engine is operating below theRPM set by the pilot. As an example, if the aircraft begins to pitchupward into a climb maneuver, the airspeed decreases across thepropeller blades. When this occurs, the RPM of the engine decreasesbelow the desired setting. During normal operation, the primary pitchcontrol valve 230 selectively controls a flow of hydraulic fluid to orfrom the pitch actuation assembly 202 to maintain the RPM of the engineas near as possible to the desired setting, or stated alternatively, tomaintain an onspeed condition.

Moreover, for this example, the primary control valve 230 is operativelyconfigured to feather the propeller blades 150 to a feathered positionbut only upon the failure of a secondary control valve (described below)and upon the occurrence of a failure condition (e.g., an engine failurecondition) or upon a user input. For example, if the torque sensor 268operatively configured to sense the output torque of the propeller shaft136 senses that the torque is below a predetermined threshold, for thisexample, the engine is determined to have experienced an engine failurecondition. When it is determined that the engine has experienced anengine failure condition and the secondary control valve has failed, theprimary control valve 230 is operatively configured to selectively allowa controlled amount of hydraulic fluid to the pitch actuation assembly202 such that the propeller blades 150 are actuated to a featheredposition. This prevents windmilling and cuts drag to a minimum.

Referring still to FIG. 3 , the pitch control unit 204 also includes asecondary pitch control valve 240. The secondary pitch control valve 240is operatively configured to take over overspeed protectionfunctionality in the event the primary control valve 230 fails, becomesunresponsive, or erroneously drives the pitch of the propeller blades150 toward a fine pitch position. In addition, the secondary pitchcontrol valve 240 is also operatively configured to feather thepropeller blades 150 to a full feather position when an engine failurecondition has been determined, which can be determined, for example, bysensing an inadequate torque output of the engine. Moreover, thesecondary pitch control valve 240 is operatively configured to providereverse enabling functionality (e.g., removal of the hydraulic lock forminimum pitch) in a way that, by design, avoids the intervention of theoverspeed functionality of the secondary pitch control valve 240.Accordingly, the secondary pitch control valve 240 of the presentdisclosure includes overspeed protection functionality, featheringfunctionality, and reverse enabling functionality. That is, overspeed,feathering, and reverse functionality is combined into and provided bythe secondary pitch control valve 240.

As shown in FIG. 3 , the secondary pitch control valve 240 is aspool-type directional EHSV. The secondary pitch control valve 240 has afirst stage 241, which is a double nozzle-flapper valve that includes atoque motor, a flapper, two nozzles, and a feedback spring. Thesecondary pitch control valve 240 also has a second stage 242, which isa precision control spool valve. The second stage 242 of the secondarypitch control valve 240 has a valve body 245 defining a chamber and aspool 243 movable within the chamber. The secondary pitch control valve240 is positioned downstream of and is in fluid communication with thehigh pressure pump 210 as well as the primary control valve 230. Inparticular, the secondary pitch control valve 240 is in fluidcommunication with the high pressure pump 210 via HP conduit 218. Aportion of the high pressure hydraulic fluid from the high pressure pump210 is delivered to the first stage 241 of the secondary pitch controlvalve 240 such that the high pressure hydraulic fluid can be used toactuate the spool 243 of the second stage 242. Moreover, hydraulic fluidcan flow from the primary control valve 230 to the secondary controlvalve 240 via a control conduit 270. The control conduit 270 splits intoa first control conduit 271 and a second control conduit 272 that feeddifferent ports of the second stage 242 of the secondary control valve240.

Depending on how the first stage 241 is controlled to actuate the spool243, the secondary control valve 240 can selectively allow a flow ofhydraulic fluid to and from the pitch actuation assembly 202. The firststage 241 controls the spool 243 of the secondary pitch control valve240 to allow the primary control valve 230 to be in fluid communicationwith the pitch actuation assembly 202 or to drain fluid from the pitchactuation assembly 202 through the drain 224 depending on the conditionin which the propeller is operating or if the engine has experienced afailure condition.

The secondary control valve 240 is fluidly connected with the oiltransfer bearing 186 as shown in FIG. 3 . Specifically, a flight conduit225 fluidly connects the secondary control valve 240 with the flightgallery 221 of the oil transfer bearing 186 and a ground conduit 226fluidly connects the secondary control valve 240 with the ground gallery222 of the oil transfer bearing 186. The beta tube 170 fluidly connectsthe flight gallery 221 with the chamber of the propeller dome 166, andmore particularly, the beta tube 170 fluidly connects the flight gallery221 with the second side 174 of the chamber of the propeller dome 166.

In the event that the primary control valve 230 fails, becomesunresponsive, or otherwise becomes inoperable, the secondary controlvalve 240 is operatively configured to take over the functionality ofthe primary control valve 230. That is, the secondary control valve 240takes over constant speed functionality, e.g., maintaining an onspeedcondition, feather functionality, and reverse enabling functionality.Accordingly, the secondary control valve 240 is adjustable between aconstant speed mode, e.g., to maintain an onspeed a condition, a feathermode, and a reverse mode and is operable to selectively allow a flow ofhydraulic fluid to or from the pitch actuation assembly 202 based atleast in part on the mode of the secondary control valve 240. Examplesare provided below.

FIGS. 4, 5, and 6 provide schematic views of the propeller control unit204 of FIG. 3 . In particular, FIG. 4 depicts the secondary controlvalve 240 in a constant speed mode, FIG. 5 depicts the secondary controlvalve 240 in a feather mode, and FIG. 6 depicts the secondary controlvalve 240 in a reverse mode. As noted above, the secondary control valve240 has valve body 245 defining a chamber 247. The spool 243 is movablewithin the chamber 247. Particularly, the spool 243 is movable between aplurality of constant speed positions in the constant speed mode (FIG. 4), one or more feather positions in the feather mode (FIG. 5 ), and oneor more reverse positions in the reverse mode (FIG. 6 ) to enable theplurality of propeller blades to rotate to a negative blade angle.Stated differently, the spool 243 is movable between a plurality ofconstant speed positions (FIG. 4 ) to operate the variable pitchpropeller assembly 106 (FIG. 2 ) in a constant speed mode, one or morefeather positions (FIG. 5 ) to operate the variable pitch propellerassembly 106 in a feather mode, and one or more reverse positions (FIG.6 ) to operate the variable pitch propeller assembly 106 in a reversemode.

As shown in FIG. 4 , the secondary control valve 240 is in a constantspeed mode. In the constant speed mode, the secondary control valve 240controls the flow of hydraulic fluid to the pitch actuation assembly 202(FIG. 3 ) to maintain an onspeed condition, e.g., by correctingoverspeed and underspeed conditions. When the second control valve 240is adjusted to the constant speed mode, the secondary control valve 240selectively allows a flow of hydraulic fluid to flow between the chamberof the propeller dome 166 (e.g., the second side 174 of the chamber)(FIG. 3 ) and the secondary control valve 240 to maintain an onspeedcondition.

More particularly, to maintain an onspeed condition, the controller 280first determines (e.g., automatically or via pilot input) whether anoverspeed or underspeed condition is present. The controller 280 causesone or more electrical signals to be routed to a torque motor 244 of thefirst stage 241 of the secondary control valve 240. The torque motor 244can include a first coil and a second coil spaced from the first coil.The first and second coils can be in electrical communication with thecontroller 280, and in some examples, a dedicated power supply (e.g., avoltage or current source). In some examples, the controller 280 canprovide the required electrical power. When the electrical signals areprovided to one or both of the coils, an electromagnetic torque isapplied to an armature of the torque motor 244 that in turn causes aflapper 246 to deflect or move between a pair of opposing nozzles 248from its resting or neutral position. Particularly, the flapper 246moves closer to one nozzle and away from the other, causing a pressuredifferential over the spool 243. The pressure differential drives thespool 243 to slide or move within the chamber of the valve body 245. Thedisplacement of the spool 243 is fed back to the flapper 246 via afeedback spring 250. The spool 243 continues to slide or move until theflow forces reach equilibrium. The secondary control valve 240 candeliver an output flow proportional to the input electrical power.

The spool 243 defines a first groove 251, a second groove 252, and athird groove 253 spaced between lands of the spool 243. When the spool243 is in the constant speed mode, the primary control valve 230 isfluidly connected with the first groove 251 via the first controlconduit 271 (as well as main control conduit 270); thus, hydraulic fluidcan flow from the primary control valve 230 into the first groove 251 ofthe spool 243 when the spool 243 is in constant speed mode. The firstgroove 251 is also fluidly connected with the flight conduit 225 in theconstant speed mode. Accordingly, hydraulic fluid can flow to the flightgallery 221 (FIG. 3 ) from the first groove 251 of the secondary controlvalve 240 (e.g., to move the control piston 168 to the left in FIG. 3 sothat propeller blades 150 are moved to a more fine pitch position), orin some instances, hydraulic fluid can flow from the flight gallery 221(FIG. 3 ) to the first groove 251 of the secondary control valve 240(e.g., to move the control piston 168 to the right in FIG. 3 so thatpropeller blades 150 are moved to a more coarse pitch position). Whenthe spool 243 is in one of the plurality of constant speed positions,the second groove 252 is not fluidly connected with the ground gallery222 (FIG. 3 ). In addition, in the constant speed mode, the groundgallery 222 is fluidly connected with a drain 274 thru the third groove253, which prevents the pitch of the blades from going below the minimumflight pitch during the flight. Drain 274 can be a common scavengedrain. Hydraulic fluid flowing along the drain 274 can be scavenged tothe lubrication supply 212, for example.

By changing the electrical power input to the torque motor 244, thespool 243 can be moved or controlled within the chamber 247 to increaseto decrease the hydraulic flow to the pitch actuation assembly 202.Stated more particularly, the amount of fluid within the second side 174of the chamber of the propeller dome 166 can be adjusted so that thecontrol piston 168 can be actuated along the axial direction A, which asnoted previously, ultimately adjusts the pitch of the propeller blades150, e.g., to a more fine or coarse pitch to maintain the onspeedcondition. When the propeller blades 150 are moved to a coarsened orhigher pitch position to compensate for an overspeed condition, thepropeller blades 150 are able to better absorb the engine power, and asa result, the engine RPM decreases to the desired setting. Consequently,the engine can return to an onspeed condition. On the other hand, whenthe propeller blades 150 are moved to a finer or lower pitch position tocompensate for an underspeed condition, the propeller blades 150 absorbless of the engine power, and as a result, the engine RPM increases tothe desired setting. Consequently, the engine can return to an onspeedcondition.

As shown in FIG. 5 , the secondary control valve 240 is in feather mode.As noted, the secondary pitch control valve 240 is operativelyconfigured to feather the propeller blades 150 to a full featherposition when an engine failure condition has been determined or via apilot input. As noted previously, when the secondary control valve 240is in feather mode, the spool 243 is movable between one or more featherpositions. For instance, as depicted in FIG. 5 , the spool 243 is movedby the torque motor 244 in a similar manner as described above to afeather position. For this example, the spool 243 is moved in adirection slightly downward relative to the position of the spool 243 inthe constant speed mode shown in FIG. 4 . The deflection of the feedbackspring 250 confirms the slight downward movement of the spool 243 inFIG. 5 .

When the secondary control valve 240 is adjusted to the feather mode,the secondary control valve 240 selectively allows the flow of hydraulicfluid to flow from the second side 174 of the chamber of the propellerdome 166 to the secondary control valve 240. More particularly, when thesecondary control valve 240 is in the feather mode and thus the spool243 is moved into one of the one or more feather positions, the primarycontrol valve 230 is not fluidly connected with the first groove 251 ofthe spool 243. Particularly, the first control conduit 271 is notfluidly connected with the first groove 251. Accordingly, no additionalhydraulic fluid can flow from primary control valve 230 to secondarycontrol valve 240 and ultimately to the second side 174 of the chamberof propeller dome 166 (FIG. 3 ). Further, as shown in FIG. 5 , thesecond groove 252 is not fluidly connected with the ground gallery 222when the spool 243 is in one of the one or more feather positions. Morespecifically, a land of the spool 243 that separates the second groove252 from the third groove 253 prevents hydraulic fluid from flowingalong the second control conduit 272 into the second groove 252 and intothe ground conduit 226 to eventually flow to the ground gallery 222.Accordingly, additional hydraulic fluid is completely cutoff fromflowing to the second side 174 of the chamber of propeller dome 166.Hydraulic fluid can be drained from the second side 174 of the chambersuch that the control piston 168 is biased by the spring 172 and thecounterweights 182 toward a full feather position (i.e., the controlpiston 168 can translate along the axial direction A to a positionfurthest to the right in FIG. 3 ). In this manner, the propeller blades150 can be adjusted to a full feather position. In feather mode, thepropeller blades 150 can cease rotation about the axial direction A, forexample. Further, as shown in FIG. 5 , the third groove 253 of the spool243 provides fluid communication between ground conduit 226 and drain274 and the first groove 251 of the spool 243 provides fluidcommunication between flight conduit 225 and drain 274. In this way,hydraulic fluid from the flight gallery 221 and ground gallery 222 canbe scavenged, e.g., to lubrication supply 212.

As shown in FIG. 6 , the secondary control valve 240 is in reverse mode.As noted, the secondary pitch control valve 240 is operativelyconfigured to reverse the pitch angle of the propeller blades 150, e.g.,to create reverse thrust. When the secondary control valve 240 is inreverse mode, the spool 243 is movable between one or more reversepositions. For instance, as depicted in FIG. 6 , the spool 243 is movedby the torque motor 244 in a similar manner as described above to areverse position. That is, for the depicted example of FIG. 6 , thespool 243 is moved in a direction slightly upward relative to theposition of the spool 243 in the constant speed mode shown in FIG. 4 .The deflection of the feedback spring 250 confirms the slight upwardmovement of the spool 243 in FIG. 6 .

When the secondary control valve 240 is adjusted to the reverse mode,the secondary control valve 240 selectively allows the flow of hydraulicfluid to flow from the secondary control valve 240 to the second side174 of the chamber (FIG. 3 ) and from the secondary control valve 240 tothe ground gallery 222. More particularly, when the secondary controlvalve 240 is in the reverse mode and thus the spool 243 is in one of theone or more reverse positions, the primary control valve 230 is fluidlyconnected with the first groove 251 of the spool 243. The first groove251 is also fluidly connected with the flight gallery 221 via the flightconduit 225 when the spool 243 is in one of the one or more reversepositions as shown in FIG. 6 . That is, in one of the reverse positions,the first groove 251 of the spool 243 fluidly connects the first controlconduit 271 and the flight conduit 225. Thus, hydraulic fluid can flowfrom the primary control valve 230 to the secondary control valve 240and ultimately to the second side 174 of the chamber of the propellerdome 166 (FIG. 3 ).

Moreover, when the secondary control valve 240 is adjusted to thereverse mode, the second groove 252 of the spool 243 fluidly connectsthe primary control valve 230 with the secondary control valve 240,e.g., via the second control conduit 272 (as well as main controlconduit 270). The second groove 252 is also fluidly connected with theground gallery 222 via the ground conduit 226 when the spool 243 is inone of the one or more reverse positions as shown in FIG. 6 . Thus,hydraulic fluid can flow from the primary control valve 230 to thesecondary control valve 240 and ultimately to the ground gallery 222.The flow of hydraulic fluid into the ground gallery 222 can enable thereverse functionality of the propeller assembly 106 (FIG. 3 ) and theflow of hydraulic fluid into the flight gallery 221 and ultimately tothe second side 174 of the chamber can fill into and force the controlpiston 168 to engage a stop 188 (FIG. 3 ) (i.e., the control piston 168is moved to a far left position in FIG. 3 by the hydraulic fluid).Moreover, in reverse mode, fluid can move from the flight gallery 221and the ground gallery 222 to the primary control valve 230. The primarycontrol valve 230 can drain the fluid (e.g., oil) to the oil system asneeded, e.g., to increase the pitch angle of the blades.

As further shown in FIG. 6 , when the spool 243 is in one of the one ormore reverse positions, the drain 274 is not fluidly connected with thefirst control conduit 271, the second control conduit 272, the flightconduit 225, or the ground conduit 226. Thus, the third groove 253 ofthe spool 243 does not fluidly connect the drain 274 with the flightgallery 221, the ground gallery 222, or the primary control valve 230when the spool 243 is in one of the one or more reverse positions.Accordingly, hydraulic fluid can flow from the primary control valve 230through first groove 251 of the spool 243 and to the flight gallery 221via flight conduit 225 without any of the hydraulic fluid draining viadrain 274. Moreover, hydraulic fluid can flow from the primary controlvalve 230 through second groove 252 of the spool 243 and to the groundgallery 222 via ground conduit 226 without any of the hydraulic fluiddraining via drain 274. In contrast, as shown in FIGS. 4 and 5 , whenthe spool 243 is in one of the one or more feather positions (FIG. 5 )or one of the plurality of constant speed positions (FIG. 4 ), the thirdgroove 253 of the spool 243 fluidly connects the ground gallery 222 withthe drain 274 via the ground conduit 226. Thus, when the spool 243 is ineither a feather or constant speed positions, at least some portion ofthe hydraulic fluid can drain from the ground gallery 222.

Returning to FIG. 3 , as noted above, the gas turbine engine 100includes a controller 280. The controller 280 is communicatively coupledwith various components of the propeller control system 200. Morespecifically, the controller 280 is communicatively coupled with aprimary speed sensor 260, a primary blade angle feedback sensor 262, asecondary speed sensor 264, a secondary blade angle feedback sensor 266,the primary pitch control valve 230, the secondary pitch control valve240, a torque sensor 268, the power lever 206, and other components ofthe propeller assembly 106. The various components of the propellercontrol system 200 can be communicatively coupled with the controller280 in any suitable manner, such as e.g., by wired or wirelesscommunication lines (shown by dashed lines in FIG. 3 ). Thecommunication between the controller 280 and the various components ofthe propeller control system 200 will be described in turn.

As shown in FIG. 3 , the controller 280 is communicatively coupled withthe primary speed sensor 260 and the primary blade angle feedback sensor262. The primary speed sensor 260 is operatively configured to sense therotational speed of the piston rod 184, the beta tube 170, or some otherrotatory component of the propeller assembly 106 that rotates in unisonabout the axial direction A with the propeller blades 150. Duringoperation, the primary speed sensor 260 sends or otherwise transmits oneor more signals indicative of the rotational speed of the propellerblades 150. The controller 280 receives or otherwise obtains the one ormore signals indicative of the rotational speed of the propeller blades150 and can compare the actual rotational speed of the propeller blades150 with the RPM set by controller 280. In this manner, the controller280 can determine whether the propeller assembly 106 is operating in anonspeed condition, an overspeed condition, or an underspeed condition.Based on the determined condition, the controller 280 can send one ormore signals to the primary control valve 230 to control the spool 233of the primary control valve 230 to selectively allow an amount ofhydraulic fluid to flow to or from the pitch actuation assembly 202 sothat the pitch of the propeller blades 150 can ultimately be adjusted.In this way, the propeller assembly 106 is maintained in or as close aspossible to an onspeed condition.

The controller 280 is also communicatively coupled with the secondaryspeed sensor 264 as well as the secondary blade angle feedback sensor266. As noted above, in the event the primary control valve 230 fails,becomes unresponsive, or erroneously drives the pitch of the propellerblades 150 toward a fine pitch position, the secondary pitch controlvalve 240 takes over operation of governing overspeed conditions as wellas feathering the propeller blades 150 to a full feather position. Thecontroller 280 then utilizes the secondary speed sensor 264 and may usethe secondary blade angle feedback sensor 266 in conjunction with thesecondary pitch control valve 240 to control the propeller assembly 106.

The secondary speed sensor 264 is operatively configured to sense therotational speed of the piston rod 184, the beta tube 170, or some otherrotational component of the propeller assembly 106 that rotates inunison about the axial direction A with the propeller blades 150. Thesecondary speed sensor 264 can continuously sense the rotational speedof the propeller blades 150. The secondary speed sensor 264 sends orotherwise transmits one or more signals indicative of the rotationalspeed of the propeller blades 150. The controller 280 receives orotherwise obtains the one or more signals indicative of the rotationalspeed of the propeller blades 150 and can compare the actual rotationalspeed of the propeller blades 150 with the RPM set in the FADEC systemfor overspeed governing. In this manner, the controller 280 candetermine whether the propeller assembly 106 is operating in an onspeedcondition, an overspeed condition, or an underspeed condition. Based onthe determined condition, the controller 280 can send one or moresignals to the secondary pitch control valve 240 to control the spool243 to selectively allow an amount of hydraulic fluid to flow to or fromthe pitch actuation assembly 202 so that the pitch of the propellerblades 150 can ultimately be adjusted. In this way, the propellerassembly 106 can be returned to an overspeed governing onspeedcondition.

To improve the accuracy and overall efficiency of the engine 100 and thepropeller assembly 106, the controller 280 can receive or otherwiseobtain one or more signals from the primary blade angle feedback sensor262 and/or the secondary blade angle feedback sensor 266. The primaryand secondary blade angle feedback sensors 262, 266 are operativelyconfigured to sense the blade angle or pitch of the propeller blades 150by measuring or sensing the axial position of the piston rod 184, thebeta tube 170, or some other rotary component that is translated alongthe axial direction A in unison with the control piston 168. One or moresignals indicative of the axial position of the piston rod 184 are sentor otherwise transmitted from the primary and/or secondary blade anglefeedback sensors 262, 266 to the controller 280. The controller 280receives or otherwise obtains the one or more signals indicative of theaxial position of the piston rod 184, and based at least in part on theaxial position of the piston rod 184, the controller 280 can determinethe blade angle of the propeller blades 150. By knowing the pitch orblade angle of the propeller blades 150, the controller 280 can ensurethat the various components of the propeller control system 200 arefunctioning properly. Moreover, the controller 280 can use the sensedinformation to improve the timing and flows of the various valves of thesystem such that the propeller control system 200 can become moreefficient and effective at adjusting the pitch of the propeller blades150.

For certain ground operations as well as inflight reverse thrustrequirements, the primary blade angle feedback sensor 262 and/or thesecondary blade angle feedback sensor 266 can sense the blade angle orpitch of the propeller blades 150 by measuring or sensing the axialposition of the piston rod 184, the beta tube 170, or some other rotarycomponent that is translated along the axial direction A in unison withthe control piston 168 in the same or similar manner as noted above. Oneor more signals indicative of the axial position of the piston rod 184can be sent or otherwise transmitted from the primary and/or secondaryblade angle feedback sensors 262, 266 to the controller 280. Thecontroller 280 receives or otherwise obtains the one or more signalsindicative of the axial position of the piston rod 184, and based atleast in part on the axial position of the piston rod 184, thecontroller 280 can determine the negative blade angle of the propellerblades 150.

FIG. 7 provides an example controller 280 of the gas turbine engine ofFIGS. 1 and 2 for controlling the propeller control system 200 in amanner as described above. The controller 280 includes variouscomponents for performing various operations and functions, such ase.g., receiving one or more signals from the sensors of the propellercontrol system 200 and the power lever 206, determining the condition ofthe propeller assembly 106 and engine 100, sending one or more signalsto the first pitch control valve 230 to control the amount of hydraulicfluid to the pitch actuation assembly 202 if the propeller is determinedto be in the overspeed condition or underspeed condition, and thesecondary control pitch valve 240 to control the amount of hydraulicfluid to the pitch actuation assembly 202 if the propeller is in anengine failure condition, a feather condition based on a pilot or userinput, etc. That is, the controller 280 controls the primary controlvalve 230 to supply/drain oil to/from the flight gallery 221 andcontrols the secondary control valve 240 to select the “working” mode incase of a failure of the primary control valve 230.

As shown in FIG. 7 , the controller 280 can include one or moreprocessor(s) 281 and one or more memory device(s) 282. The one or moreprocessor(s) 281 can include any suitable processing device, such as amicroprocessor, microcontroller, integrated circuit, logic device,and/or other suitable processing device. The one or more memorydevice(s) 282 can include one or more computer-readable media,including, but not limited to, non-transitory computer-readable media,RAM, ROM, hard drives, flash drives, and/or other memory devices.

The one or more memory device(s) 282 can store information accessible bythe one or more processor(s) 281, including computer-readableinstructions 284 that can be executed by the one or more processor(s)281. The instructions 284 can be any set of instructions that whenexecuted by the one or more processor(s) 281, cause the one or moreprocessor(s) 281 to perform operations. In some examples, theinstructions 284 can be executed by the one or more processor(s) 281 tocause the one or more processor(s) 281 to perform operations, such asany of the operations and functions for which the controller 280 orcontrollers are configured, such as e.g., receiving one or more signalsfrom sensors and determining an axial position of the beta tube 170 suchthat the blade angle of the propeller blades 150 can be determined. Theinstructions 284 can be software written in any suitable programminglanguage or can be implemented in hardware. Additionally, and/oralternatively, the instructions 284 can be executed in logically and/orvirtually separate threads on processor(s) 281.

The memory device(s) 282 can further store data 283 that can be accessedby the one or more processor(s) 281. The data 283 can also includevarious data sets, parameters, outputs, information, etc. shown and/ordescribed herein. The controller 280 can also include a communicationinterface 285 used to communicate, for example, with other components ofan aircraft in which the gas turbine engine 100 is mounted to, such ase.g., another controller configured to control another engine of theaircraft. The communication interface 285 can include any suitablecomponents for interfacing with one or more network(s), including forexample, transmitters, receivers, ports, controllers, antennas, and/orother suitable components.

As shown further in FIG. 7 , the controller 280 includes primary logic286 and secondary logic 287. Although the primary logic 286 and thesecondary logic 287 are shown as separate from the one or moreprocessor(s) 281 and the one or more memory device(s) 282, the primaryand secondary logic 286, 287 can be embodied in the one or moreprocessor(s) 281 and the one or more memory device(s) 282 describedabove. The primary logic 286 is operatively configured to control theprimary control valve 230. The secondary logic 287 is operativelyconfigured to control the secondary pitch control valve 240. Inparticular, the secondary logic 287 includes a constant speed logicmodule 288, a feathering logic module 289, and a reverse logic module290. The constant speed logic module 288 provides controller 280 withthe logic to control the secondary pitch control valve 240 in actuatingthe propeller blades 150, e.g., to a higher more coarse pitch toultimately move propeller assembly 106 from an overspeed condition togoverning to a selected speed condition. Likewise, the feathering logicmodule 289 provides controller 280 with the logic to control thesecondary pitch control valve 240 in actuating the propeller blades 150to a full feather position when an engine failure condition has beendetermined by the controller 280 or upon a user or pilot input. Further,the reverse logic module 290 provides controller 280 with the logic tocontrol the secondary pitch control valve 240 in actuating the propellerblades 150 to a negative pitch position when a reverse condition hasbeen determined by the controller 280 or upon a user or pilot input.

During operation, the powerplant, such as e.g., the engine 100 of FIGS.1 and 2 , defines an axial direction and a radial direction. The enginehas a controller, such as e.g., controller 280 described herein. Thevariable pitch propeller assembly has a plurality of propeller bladesrotatable about the axial direction and adjustable about respectivepitch axes each extending along the radial direction. The propellercontrol system has a pitch actuation assembly for actuating thepropeller blades about their respective pitch axes and a pitch controlunit for driving the pitch actuation assembly. The pitch control unithas a primary control valve and a secondary control valve bothcommunicatively coupled with the controller. The primary control valveand the secondary control valve are each configured to selectivelycontrol a flow of hydraulic fluid to or from the pitch actuationassembly. For instance, the primary control valve can control the flowof hydraulic fluid during normal operation. The secondary control valvecan control the flow of hydraulic fluid to the pitch actuation assemblywhen the primary control valve fails or otherwise becomes unresponsive.In this way, the secondary control valve acts as a failsafe.

The controller can receive one or more operational parameters of thepowerplant. For instance, in some example implementations, the one ormore operational parameters can be indicative of a power setting of thepowerplant. The one or more operational parameters indicative of thepower setting of the powerplant can be obtained by the controller 280.The power lever 206, or an angular position sensor device, can send oneor more signals indicative of the angle of the power lever 206. Based onthe angle of the power lever 206, the controller 280 can determine thepower setting selected by the pilot. As another example, the powersetting selected by the pilot can be digitized, and thus, the powersetting can be transmitted to the controller 280 digitally.

In some example implementations, the one or more operational parameterscan be indicative of the rotational speed of the propeller blades 150about the axial direction A. For instance, the rotational speed of thepropeller blades 150 can be determined by the controller 280 based onone or more signals from the primary speed sensor 260 and/or thesecondary speed sensor 264. The primary or secondary speed sensors 260,264 can sense or measure the rotational speed of a rotary component,such as, e.g., the piston rod 184, the beta tube 170, or some otherrotary component that rotates about the axial direction A in unison withthe propeller blades 150.

In some example implementations, the one or more operational parameterscan be indicative of a torque output of the powerplant. For instance,the torque sensor 268 positioned proximate the propeller shaft 136 (FIG.3 ) can sense the torque output of the core turbine engine 104 of thepowerplant. One or more signals indicative of the torque output can berouted to the controller 280.

In some example implementations, the one or more operational parameterscan be indicative of an angular position of a condition lever or aselected condition of the powerplant. For instance, the cockpit of theaircraft or vehicle in which the turboprop and propeller assembly aremounted can include a condition lever. A pilot or crew member canselectively adjust the condition lever to select a condition of thepropeller assembly. For instance, the angular position of the conditionlever can be indicative of a reverse mode or a feather mode.

The controller can determine a condition of the powerplant based atleast in part on the one or more operational parameters. For example,the condition could be one of an overspeed condition, an underspeedcondition, a feather condition or an engine or powerplant failurecondition, a reverse thrust condition, etc.

For example, in implementations in which the one or more operationalparameters are indicative of the rotational speed of the propellerblades 150 about the axial direction A, the rotational speed of thepropeller blades 150 can be determined and compared to the powersetting. In this way, the controller 280 can determine whether thepowerplant or engine is operating in an onspeed condition, an underspeedcondition, or an overspeed condition. Once the condition of thepowerplant or engine is known, the propeller control system 200 can makethe necessary adjustments to the pitch of the propeller blades 150, e.g.

As another example, in implementations in which the one or moreoperational parameters are indicative of a torque output of thepowerplant can include comparing the power setting with the torqueoutput of the powerplant. If the torque output of the powerplant is ator below a predetermined threshold for the given power setting, thecontroller 280 can determine that a powerplant or engine failurecondition has occurred. When such a powerplant failure condition hasbeen determined, the controller 280 can send one or more signals to theprimary control valve 230 to actuate the primary control valve 230 suchthat the propeller blades 150 are actuated to a fully featheredposition. If, however, the primary control valve 230 fails or isotherwise unresponsive, the controller 280 can send one or more signalsto the secondary control valve 240 to actuate the secondary controlvalve 240 such that the propeller blades 150 are actuated to a fullyfeathered position.

As a further example, in implementations in which the one or moreoperational parameters are indicative of an angular position of acondition lever or a selected condition of the powerplant can includedetermining the condition of the powerplant based at least in part onthe angular position of the condition lever or the selected user input.

At, the method includes controlling, by the controller, the secondarycontrol valve adjustable between a constant speed mode, a feather mode,and a reverse mode to selectively allow a controlled amount of hydraulicfluid to or from the pitch actuation assembly based at least in part onthe condition determined. For instance, the spool 243 of the secondarycontrol valve 240 of FIGS. 4, 5, and 6 can be moved to selectively allowa controlled amount of hydraulic fluid to or from the pitch actuationassembly based at least in part on the condition determined. Forinstance, if an overspeed condition or feather condition (e.g., anengine failure condition) is determined, hydraulic fluid can be drainedfrom the pitch actuation assembly in a manner described herein. If, areverse thrust condition is determined, the hydraulic fluid can bedirected to the flight gallery 221 and the ground gallery 222 to enablereverse functionality and to actuate the control piston 168 to a morefine position such that the propeller blades are ultimately pitched to areverse angle.

It will be understood that the pitch control unit 204 provides highpressure hydraulic actuation oil flow and controls propeller pitch anglein response to commands. FIG. 8 illustrates the primary pitch controlvalve 230, which as previously described is a torque motor driven doublestage valve. During operation torque motor shifts the flapper 246, whichthen operates to shift the spool 233. FIG. 8 illustrates the primarypitch control valve 230 with a variety of current inputs, withcorresponding spool positions and flow to and from the propeller dome166 (FIG. 3 ).

When the electrical signals are provided to one or both of the coils, anelectromagnetic torque is applied to an armature of the torque motor 244that in turn causes a flapper 246 to deflect or move between a pair ofopposing nozzles 248 from its resting or neutral position, which isshown at the primary pitch control valve 230 a. As can be seen in theneutral position with no current supplied, the flow to the drain line224 from the main control conduit 270 is minimal. The primary pitchcontrol valve 230 b shows the assembly with negative 80 miliamps ofcurrent provided, as illustrated the flow through the drain line 224 isfully open from the main control conduit 270. The primary pitch controlvalve 230 c shows the assembly with positive 80 miliamps of currentprovided, as illustrated the flow through the drain line 224 is closedand fluid is supplied from the supply conduit to the main controlconduit 270.

As explained above, when it is determined that the engine hasexperienced an engine failure condition and the secondary control valvehas failed, the primary control valve 230 is operatively configured toselectively allow a controlled amount of hydraulic fluid to the pitchactuation assembly 202 such that the propeller blades 150 are actuatedto a feathered position. However, if no pressurized oil is available theprimary pitch control valve 230 moves to drain for all current inputs.If there is an oil starvation condition, the primary pitch control valve230, for any electrical current supplied, fluidly couples the flightgallery line 221 to the drain 224. In this way the oil is drained fromthe dome and an unwanted engine thrust loss occurs.

Again, a neutral input when no oil is supplied will results in a minimalflow to the drain line 224 as illustrated as 230 d. The primary pitchcontrol valve 230 e shows the assembly with negative 80 miliamps ofcurrent provided, as illustrated the flow through the drain line 224 isnegligibly open from the main control conduit 270. The primary pitchcontrol valve 230 f shows the assembly with positive 80 miliamps ofcurrent provided, as illustrated the flow through the drain line 224 isopen and fluid is supplied from the main control conduit 270. Thecontroller 280 when the pitch begins to go down, tries to supply oil tothe primary pitch control valve 230 and commands a positive current,this in turn drains to the maximum.

The primary pitch control valve 230 needs oil flow to properly lead thepropeller pitch. When there is not enough pressure or flow to the firststage of the primary pitch control valve 230, the primary pitch controlvalve 230 is not able to work correctly. Instead, the primary pitchcontrol valve 230 drains oil from the propeller dome 166 and acoarsening forward feather occurs. The propeller control system 200including the primary pitch control valve 230 is not able todiscriminate between a temporary oil starvation such as when negativeg-force occurs for a few seconds from an actual failure or a more severeevent; either occurrence will move the propeller assembly 106 in featherposition.

It has been determined that the inclusion of a one-way-relief valve inthe pitch control unit will be able to maintain the control conduit ofthe pitch control valve with a sufficient pressure for a longer time.FIG. 9 illustrates a propeller control system 300 for controlling thepropeller assembly 106 of the gas turbine engine 100 of FIGS. 1 and 2and only a portion of which is shown in FIG. 9 . The propeller controlsystem 300 includes similar components as described for the propellercontrol system 200; therefore, like parts will be identified with likenumerals in the 300 series with it being understood that the descriptionof the like parts applies to the accessory tool 400, unless otherwisenoted. The propeller assembly 106 is the same even though only a portionis illustrated.

As with the propeller control system 200, the propeller control system300 includes a pitch actuation assembly 302, a pitch control unit 304,and controller 380. The propeller control system 300 also operates in asimilar manner to that of the propeller control system 200.

One difference is the inclusion of an oil starvation valve 356 having aninlet 357 and an outlet 358. The oil starvation valve 356 canselectively fluidly coupled the flow of hydraulic fluid from thepropeller dome 166 via the flight conduit 325 to the pitch control unit304. While the oil starvation valve 356 has been illustrated anddescribed herein as a one-way-relief valve it will be understood thatany suitable valve mechanism can be utilized.

Another difference is the inclusion of a dome pressure limiting valve354 that fluidly connects the flight conduit 325 and flight gallery 321with the drain 324 such that the hydraulic fluid can be selectivelyscavenged, e.g., to lubrication supply 312. The dome pressure limitingvalve 354 can be any suitable valve including a one-way valve thatblocks the blow of fluid to the drain 324. During operation, the domepressure limiting valve 354 can operate as a relief valve when pressurein the propeller dome 166 exceeds a predetermined threshold.

During operation, depending on how the first stage 341 of the primarypitch control valve 330 is controlled to actuate the spool 343, thesecondary control valve 340 can selectively allow a flow of hydraulicfluid to and from the pitch actuation assembly 302. The inclusion of theadditional valving does not have an effect on the operation of thepropeller control system 300 when oil is available at the inlet ports ofthe primary pitch control valve 330. The primary pitch control valve 330a is shown at a resting or neutral position when no current is suppliedand the oil starvation valve 356 a is closed. The flow to the drain line324 from the main control conduit 370 is minimal. The primary pitchcontrol valve 330 b shows the assembly with negative 80 miliamps ofcurrent provided and as illustrated the flow through the drain line 224is fully open from the main control conduit 270 and the oil starvationvalve 356 b is closed. The primary pitch control valve 330 c shows theassembly with positive 80 miliamps of current provided, as illustratedthe flow through the drain line 324 is closed and fluid is supplied fromthe supply conduit to the main control conduit 270, the oil starvationvalve 356 c is also closed.

However, in the event that no oil is available at the inlet port ornozzles 348 of the primary pitch control valve 330 during operation ofthe propeller control system 300 the oil starvation valve 356 can beused to supply oil from the propeller dome 166 to first stage 341 of theprimary pitch control valve 330 and to avoid going into feather toofast. In such an instance, the pitch control unit 304 internal pressuregoes down and oil starvation valve 356 opens as illustrated at 356 d,356 e, and 356 f. In this manner the flight gallery line 321 and fluidconduit 325 are fluidly coupled via the oil starvation valve 356 to thefirst stage 341 of the primary pitch control valve 330. Thus, oil isprovided and the spool 343 of the first stage 341 of the primary pitchcontrol valve 330 doesn't move to drain oil from the propeller dome 166if not required. In this manner, even during an oil starvationcondition, the primary pitch control valve 330 and the propeller controlsystem 300 can continue to operate as if an oil starvation conditionwere not occurring although it will be understood that the amount of oilused to supply oil to the first stage 341 of the primary pitch controlvalve 330 is lower if compared with the oil drained by the primary pitchcontrol valve 330 if the first stage 341 of the primary pitch controlvalve 330 is without oil.

During operation in an oil starvation condition a range of current canstill be provided and depending on how the first stage 341 of theprimary pitch control valve 330 is controlled to actuate the spool 343,the secondary control valve 340 can selectively allow a flow ofhydraulic fluid to and from the pitch actuation assembly 302. While theoil starvation valve 356 d is open, the primary pitch control valve 330d is shown at a resting or neutral position when no current is suppliedand the oil and flow to the drain line 324 from the main control conduit370 is minimal. While the oil starvation valve 356 e is open, theprimary pitch control valve 330 e shows the assembly with negative 80miliamps of current provided and as illustrated the flow through thedrain line 224 is fully open from the main control conduit 270. Finally,when the oil starvation valve 356 f is open, the primary pitch controlvalve 330 f shows the assembly with positive 80 miliamps of currentprovided and the flow through the drain line 324 is closed and fluid issupplied from the supply conduit to the main control conduit 270.

Aspects of the propeller control system 300 provide a variety ofbenefits including that the one-way relief valve supplies oil to thefirst stage of the primary pitch control valve in oil starvation eventsand provides an internal, inexpensive, and lightweight solution to allowthe primary pitch control valve to use the propeller dome oil toproperly command the primary pitch control valve. Eventually, thepropeller blades move to feather but with a lower speed if compared witha solution without the oil's starvation valve. The propeller controlsystem 300 avoids the feather mode in case of short time, such as by wayof non-limiting examples 5 seconds or less, oil starvation events suchas those caused by negative g-force maneuvers. The oil starvation valve356 also controls the oil flow from the propeller dome 166 to the pitchcontrol unit 304 as just the oil needed to command the first stage 341of the primary pitch control valve 330 is needed. While there is amovement of the blade 150 to a greater pitch angle, the full feathermode doesn't occur. The inclusion of the oil starvation valve 356 allowsa lower thrust loss if compared with the solution without the oilstarvation valve.

It will be understood that additional methods and alternative pitchcontrol units can be utilized to ensure that the control valves operatecorrectly during oil starvation. By way of additional non-limitingexample, FIG. 11 illustrates a propeller control system 400 forcontrolling the propeller assembly 106 of the gas turbine engine 100 ofFIGS. 1 and 2 . The propeller control system 400 includes similarcomponents as described for the propeller control system 200; therefore,like parts will be identified with like numerals in the 400 series withit being understood that the description of the like parts applies tothe accessory tool 400, unless otherwise noted. The propeller assembly106 is the same even though only a portion is illustrated.

As with the propeller control system 200, the propeller control system400 includes a pitch actuation assembly 402, a pitch control unit 404,and controller 480. The propeller control system 400 also operates in asimilar manner to that of the propeller control system 200.

One difference is that a pitch lock valve 456 and a solenoid valve 458have been illustrated as being included in the pitch control unit 404.The pitch lock valve 456 selectively fluidly couples the primary pitchcontrol valve 430 and secondary pitch control valve 440 to the flightgallery 421. More specifically, the pitch lock valve 456 is located onthe flight conduit 425 between the components. An inlet 456 a to thepitch lock valve 456 is fluidly coupled to the flight gallery 421. Afirst outlet 456 b fluidly couples the primary pitch control valve 430.A second outlet 456 c fluidly couples the secondary pitch control valve440. A third outlet 456 d is fluidly coupled with a fluid cavity 459 ofthe solenoid valve 458. A valve body 457 is moveable to a first positionto selectively fluidly couple the inlet 456 a to the first outlet 456 band second outlet 456 c or to a second position to fluidly couple theinlet 456 a or to the third outlet 456 d. In this manner the pitch lockvalve 456 can simultaneously, in case of oil starvation, stops the oilflow forward the primary pitch control valve 430 and secondary pitchcontrol valve 440 and locks the blade positions of the propellerassembly 106 based on a change in pressure. More specifically whenpressure reduces within the pitch control unit 404, the valve body 457can move from the first position in FIG. 11 to the second position asillustrated in FIG. 12 . Hydraulic pressure at the port 455, coupled tothe propeller gearbox drain line 424 a, can provide the force to movethe valve body 457 to the second position.

Adding only a hydraulic pitch lock valve 456 to lock the pitch would notallow the pitch control unit 404 to discriminate if there was atemporary oil starvation or a serious failure. Therefore, to preservethe possibility to feather the propeller assembly 106, in all theconditions, the solenoid valve 458 has been added. The solenoid valve458 maintains the possibility to drain oil from the propeller dome 166and allow the feather mode based on user selection. The solenoid valve458 can be a suitable electro-valve having a moveable spool 461 within afluid cavity 459 that is solenoid commanded to maintain the ability tofeather if needed. The solenoid valve 458 can be communicatively coupledwith the controller 480, the FADEC, and/or any suitable controlmechanism including an actuator within the aircraft. The moveable spool461 can be operable between a closed or first position, as illustratedin FIG. 11 and an opened or second position as illustrated in FIG. 12 .In the opened position, the moveable spool 461 moves to allow the fluidcavity 459 to be fluidly coupled with the propeller gearbox drain line424 a.

The pitch control unit 404 is also illustrated as including a domepressure limiting valve 454 although that need not be the case. The domepressure limiting valve 454 fluidly connects the flight conduit 425 andflight gallery 421 with the drain 424 a such that the hydraulic fluidcan be selectively scavenged, e.g., to lubrication supply 412. Duringoperation, the dome pressure limiting valve 454 can operate as a reliefvalve when pressure in the propeller dome 166 exceeds a predeterminedthreshold.

Typically, if oil starvation occurs, the current primary control valveopens the propeller dome to the drain and the assembly goes into feathermode. However, with the pitch control unit 404, if there is an oilstarvation condition, the internal pressure goes down in the pitchcontrol unit 404 and the pitch lock valve 456 locks, interrupts, orotherwise selectively fluidly closes the flight conduit 425. In thismanner, if the primary pitch control valve 430 tries to drain oil fromthe propeller dome 166, the blade pitch is locked to the last value.

Further, during oil starvation, with the pitch control unit 404 if thefeather mode is commanded, the solenoid valve 458 moves the spool 461and oil is drained from propeller dome 166 to the propeller gearboxdrain line 424 a allowing for the feathering.

Further still, while not illustrated it is contemplated that thepressure relief valve 416 and the pitch lock valve 456 can be integratedinto a single valve body or valve mechanism to save on weight, space, orexpense.

Aspects of the present disclosure provide a variety of benefitsincluding limiting or forestalling undesired forward feathering of thepropeller blades during an oil starvation event. To avoid the feathermode in case of short time, such as 5 seconds, oil starvation events apitch control lock valve is included. In this manner, if oil starvationis temporary then undesired forward feathering of the propeller blade isavoided; however, if required the pilot or FADEC can command anemergency feathering via the solenoid valve.

To the extent not already described, the different features andstructures of the various examples can be used in combination with eachother as desired. That one feature is not illustrated in all of theexamples is not meant to be construed that it cannot be, but is done forbrevity of description. Thus, the various features of the differentaspects can be mixed and matched as desired to form new aspects, whetheror not those are expressly described. All combinations or permutationsof features described herein are covered by this disclosure.

Further aspects of the invention are provided by the subject matter ofthe following clauses:

1. A variable pitch propeller assembly for an engine defining an axialdirection, a radial direction, and a circumferential direction, thevariable pitch propeller assembly comprising:

-   -   a plurality of propeller blades rotatable about the axial        direction and spaced apart along the circumferential direction,        each propeller blade of the plurality of propeller blades        rotatable through a plurality of blade angles about respective        pitch axes each extending in the radial direction;    -   a pitch actuation assembly for adjusting the plurality of        propeller blades through the plurality of blade angles and        including a propeller dome defining a chamber; and    -   a pitch control unit, comprising:    -   at least one electrohydraulic servovalve operable to selectively        allow a flow of hydraulic fluid to or from the propeller dome of        the pitch actuation assembly and when hydraulic fluid is not        located at an inlet port of the at least one electrohydraulic        servovalve an oil starvation condition is defined; and at least        one valve selectively fluidly coupling the propeller dome to the        inlet port of the at least one electrohydraulic servovalve.

2. The variable pitch propeller assembly of any preceding clause whereinthe at least one valve is a one-way valve having an inlet fluidlycoupled to the propeller dome and an outlet fluidly coupled to the inletport of the at least one electrohydraulic servovalve and during the oilstarvation condition the one-way valve is configured to fluidly couplethe propeller dome to the inlet port of the at least oneelectrohydraulic servovalve.

3. The variable pitch propeller assembly of any preceding clause whereinthe at least one electrohydraulic servovalve is a primary pitch controlvalve having a first stage and a second stage and the one-way valve isselectively fluidly coupled with the first stage.

4. The variable pitch propeller assembly of any preceding clause whereinthe plurality of propeller blades move to a feather mode during the oilstarvation condition at a lower speed as compared the pitch control unitwithout the at least one valve.

5. The variable pitch propeller assembly of any preceding clause whereinthe at least one valve is a pitch lock valve having an inlet fluidlycoupled to the propeller dome and a set of outlets and during the oilstarvation condition the pitch lock valve is configured to fluidlyuncouple the propeller dome to the inlet port of the at least oneelectrohydraulic servovalve.

6. The variable pitch propeller assembly of any preceding clause whereinthe at least one electrohydraulic servovalve comprises a primary controlvalve operable to selectively allow the flow of hydraulic fluid to orfrom the pitch actuation assembly and a secondary control valveadjustable between a constant speed mode, a feather mode, and a reversemode and operable to selectively allow the flow of hydraulic fluid to orfrom the pitch actuation assembly based at least in part on the mode ofthe secondary control valve.

7. The variable pitch propeller assembly of any preceding clause whereinthe set of outlets includes a first outlet fluidly coupled to a firststage of the primary control valve, a second outlet fluidly coupled to afirst stage of the secondary control valve, and a third outlet fluidlycoupled a drain line.

8. The variable pitch propeller assembly of any preceding clause whereinthe pitch lock valve includes a valve body moveable between a firstposition wherein the first outlet and the second outlet are fluidlycoupled with the inlet and a second position wherein the third outlet isfluidly coupled to the inlet.

9. The variable pitch propeller assembly of any preceding clause whereinthe valve body is configured to be moveable from the first position tothe second position based on a decrease in internal pressure causedduring the oil starvation condition.

10. The variable pitch propeller assembly of any preceding clause,further comprising a solenoid valve fluidly coupled between the thirdoutlet and the drain line and operable to selectively open and close aflow of hydraulic fluid through the drain line.

11. The variable pitch propeller assembly of any preceding clausewherein the solenoid valve is one of user actuated or automaticallycontroller actuated.

12. The variable pitch propeller assembly of any preceding clausewherein actuation of the solenoid valve opens the flow of hydraulicfluid through the drain line.

13. The variable pitch propeller assembly of any preceding clausewherein the secondary control valve includes a valve body defining achamber and a spool movable within the chamber and where the spooldefines a first groove and a second groove, and wherein the primarycontrol valve is fluidly connected with the first groove when the spoolis in at least one constant speed position or in at least one reverseposition.

14. The variable pitch propeller assembly of any preceding clausewherein the pitch actuation assembly further comprises:

-   -   a control piston translatable within the propeller dome;    -   a piston rod connected to the control piston and extending into        a propeller gear box of the engine, the piston rod translatable        in unison with the control piston;    -   an oil transfer bearing surrounding the piston rod within the        propeller gear box of the engine and defining a flight gallery        fluidly connected with the secondary control valve and a ground        gallery fluidly connected with the secondary control valve; and    -   a beta tube enclosed within the piston rod and fluidly        connecting the flight gallery with the chamber of the propeller        dome.

15. The variable pitch propeller assembly of any preceding clausewherein a flight gallery conduit fluidly connects the secondary controlvalve with the flight gallery and a ground gallery conduit fluidlyconnects the secondary control valve with the ground gallery.

16. A method for controlling a variable pitch propeller assembly drivenby a powerplant, the powerplant defining an axial direction and a radialdirection and comprising a controller, the variable pitch propellerassembly having a plurality of propeller blades rotatable about theaxial direction and adjustable about respective pitch axes eachextending along the radial direction, a propeller control systemcomprising a pitch actuation assembly for actuating the propeller bladesabout their respective pitch axes and a pitch control unit for drivingthe pitch actuation assembly and comprising a primary control valve anda secondary control valve both communicatively coupled with thecontroller, the primary control valve and the secondary control valveeach configured to selectively control a flow of hydraulic fluid to orfrom the pitch actuation assembly, the method comprising:

-   -   operating the powerplant;    -   controlling, by the controller, the secondary control valve        adjustable between a constant speed mode, a feather mode, and a        reverse mode to selectively allow a controlled amount of        hydraulic fluid to or from the pitch actuation assembly; and    -   selectively diverting, during an oil starvation condition,        hydraulic fluid from a propeller dome of the variable pitch        propeller assembly via at least one valve.

17. The method of of any preceding clause wherein the at least one valveis a one-way valve having an inlet fluidly coupled to the propeller domeand an outlet fluidly coupled to an inlet port of the primary controlvalve and during the oil starvation condition the one-way valve providesfluidly coupling from the propeller dome to the inlet port of theprimary control valve.

18. The method of of any preceding clause further comprising controllinga feathering with the primary control valve upon a failure of thesecondary control valve.

19. The method of any preceding clause wherein the at least one valve isa pitch lock valve having an inlet fluidly coupled to the propellerdome, a first outlet fluidly coupled to a first stage of the primarycontrol valve, a second outlet fluidly coupled to a first stage of thesecondary control valve, and a third outlet fluidly coupled a drain lineand where selectively diverting the hydraulic fluid comprises moving avalve body moveable between a first position wherein the first outletand the second outlet are fluidly coupled with the inlet or a secondposition wherein the third outlet is fluidly coupled to the inlet.

20. The method of any preceding clause wherein selectively diverting thehydraulic fluid from the propeller dome further includes opening a valveon the drain line to create a feather condition.

This written description uses examples to disclose the innovation,including the best mode, and also to enable any person skilled in theart to practice the innovation, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeis defined by the claims, and can include other examples that occur tothose skilled in the art. Such other examples are intended to be withinthe scope of the claims if they have structural elements that do notdiffer from the literal language of the claims, or if they includeequivalent structural elements with insubstantial differences from theliteral languages of the claims.

What is claimed is:
 1. A propeller controller comprising: at least oneelectrohydraulic servovalve operable to selectively allow a flow ofhydraulic fluid to or from a propeller dome; and at least one valveselectively fluidly coupling the propeller dome to an inlet port of theat least one electrohydraulic servovalve, wherein the at least one valveincludes a one-way valve having an inlet fluidly coupled to thepropeller dome and an outlet fluidly coupled to the inlet port of the atleast one electrohydraulic servovalve and, the one-way valve having anopen position and a closed position, the one-way valve in the openposition supply hydraulic fluid from the propeller dome to the inletport of the at least one electrohydraulic servovalve at a firsthydraulic pressure at the inlet port, the one-way valve in the closedposition to not supply hydraulic fluid from the propeller dome to theinlet port of the at least one electrohydraulic servovalve at a secondhydraulic pressure at the inlet port, the first hydraulic pressure lessthan the second hydraulic pressure.
 2. The propeller controller of claim1, further including a plurality of propeller blades rotatable about anaxial direction and spaced apart along a circumferential direction, eachpropeller blade of the plurality of propeller blades rotatable through aplurality of blade angles about respective pitch axes each extending ina radial direction.
 3. The propeller controller of claim 2, furtherincluding a pitch actuation assembly for adjusting the plurality ofpropeller blades through the plurality of blade angles and including thepropeller dome, the propeller dome defining a chamber.
 4. The propellercontroller of claim 2, wherein the plurality of propeller blades move toa feather mode during an oil starvation condition at a lower speed thanwithout the at least one valve.
 5. The propeller controller of claim 1,wherein the at least one electrohydraulic servovalve is a primary pitchcontrol valve having a first stage and a second stage and the one- wayvalve is selectively fluidly coupled with the first stage.
 6. Thepropeller controller of claim 1, wherein the at least oneelectrohydraulic servovalve comprises a primary control valve operableto selectively allow the flow of hydraulic fluid to or from a pitchactuation assembly and a secondary control valve adjustable between aconstant speed mode, a feather mode, and a reverse mode and operable toselectively allow the flow of hydraulic fluid to or from the pitchactuation assembly based at least in part on the mode of the secondarycontrol valve.
 7. The propeller controller of claim 6, wherein thesecondary control valve includes a valve body defining a chamber and aspool movable within the chamber and where the spool defines a firstgroove and a second groove, and wherein the primary control valve isfluidly connected with the first groove when the spool is in at leastone constant speed position or in at least one reverse position.
 8. Thepropeller controller of claim 6, further including a pitch actuationassembly including: a control piston translatable within the propellerdome; a piston rod connected to the control piston and extending into apropeller gear box of an engine, the piston rod translatable in unisonwith the control piston; an oil transfer bearing surrounding the pistonrod within the propeller gear box of the engine and defining a flightgallery fluidly connected with the secondary control valve and a groundgallery fluidly connected with the secondary control valve; and a betatube enclosed within the piston rod and fluidly connecting the flightgallery with a chamber of the propeller dome.
 9. The propellercontroller of claim 8, wherein a flight gallery conduit fluidly connectsthe secondary control valve with the flight gallery and a ground galleryconduit fluidly connects the secondary control valve with the groundgallery.
 10. A method for controlling a variable pitch propellerassembly driven by a powerplant, the method comprising: operating thepowerplant; controlling, using a controller, a first electrohydraulicservovalve adjustable between a constant speed mode, a feather mode, anda reverse mode to selectively allow a controlled amount of hydraulicfluid to or from a pitch actuation assembly of the variable pitchpropeller assembly; and selectively diverting, during an oil starvationcondition, hydraulic fluid from a propeller dome of the variable pitchpropeller assembly via a one-way valve, the one-way valve having aninlet fluidly coupled to the propeller dome and an outlet fluidlycoupled to an inlet port of a second electrohydraulic servovalve and,wherein, during an oil starvation condition, the one-way valve in anopen position to supply hydraulic fluid from the propeller dome to theinlet port of the second electrohydraulic servovalve, when an oilstarvation condition is not present, the one-way valve in a closedposition to not supply hydraulic fluid from the propeller dome to theinlet port of the second electrohydraulic servovalve.
 11. The method ofclaim 10, further including controlling a feathering with the secondelectrohydraulic servovalve upon a failure of the first electrohydraulicservovalve.
 12. The method of claim 10, wherein selectively divertingthe hydraulic fluid from the propeller dome further includes opening avalve on a drain line to create a feather condition.